Novel high peel strength rubber/textile composites

ABSTRACT

A composition for the promotion of adhesion between a rubber formulation and a textile substrate is provided. The inventive composition comprises either a mixture of specific amine functional silanes and organo-functional silanes having reactive groups or groups with an affinity for rubber. The inventive method entails the use of the inventive composition or a silane compound having both an amine moiety and a reactive group having an affinity for rubber formulations, particularly an unsaturated carbon-carbon bond. The composition may be utilized to adhere any standard reinforcement-type textile, such as polyester or polyamide, to a standard rubber composition, such as SBR, NBR, or EPDM. A method for adhering textiles to rubber formulations is also provided involving a pre-dip, -spray, -coat, and the like, of the inventive composition on a reinforcement-type textile surface followed by the contacting of the rubber formulation. Optionally, and preferably, the process involves the extra utilization of resorcinol-formaldehyde latex as an effective bonding agent to improve the adhesion between the two layers. The resulting textile-reinforced rubber product may be utilized as an automobile fan or timing belt, an automobile tire component, and any other rubber article which requires long-lasting, durable textile reinforcement.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of co-pending application Ser.No. 09/461,274, which is a continuation of application Ser. No.09/037,092, filed on Mar. 9, 1998, now U.S. Pat. No. 6,046,242.

FIELD OF THE INVENTION

[0002] This invention relates to adhesion promotion compositions whichprovide excellent adhesive characteristics between rubber and textilesubstrates. Such compositions comprise specific mixtures of aminosilanesand other organosilanes or specific compounds having both an aminosilanemoiety and a group having an affinity for rubber compositions. Theseinventive compositions may be utilized to activate a textile surface forfurther contact with a rubber alone or a resorcinol-formaldehyde latex(RFL) or similar type of adhesive compound to which a rubber maysubsequently be adhered. The methods utilizing these particular adhesionpromotion compositions are also contemplated within this invention.

DISCUSSION OF THE PRIOR ART

[0003] It has long been known that adhering a textile, particularly onecomposed of filaments having high tenacity to a rubber enhances themodulus and tensile strength of the rubber component and provideslong-lasting durability, particularly in high friction applications.Examples of such applications include fan and timing belts withinautomobile engines; vehicle tires; conveyor belts; and the like. Themain requirement of such textile-reinforced rubber articles has been thestrength of adhesion between the textile and the rubber. Without anyprimer treatment, the textile will not effectively adhere to the rubber.A weak bond between the two components results in separation of the twolayers and mechanical failure of the resulting composite. Thus, it hasbeen and is necessary to provide a textile treatment to enhance theadhesion of these two distinct components.

[0004] Previous methods of providing such adherence between rubber andtextile layers include coating or impregnating the textile layer with aformaldehyde latex (such as a resorcinol-formaldehyde vinyl-pyridinerubber latex or RFL), pre-coating with an RFL latex and an aminofunctional polyacrylate, as in U.S. Pat. No. 5,654,099, to Pelton, andin European Patent Application 665,390, to Tsubakimoto Chain Company, orutilizing a pre-activated textile which has reactive pendant groups tofacilitate adhesion between the fabric surface and the reactive sites onthe rubber layer, all of the aforementioned references being hereinentirely incorporated by reference. The RFL coating method results in acomposition which does not always provide sufficient adhesion betweenlayers. Pre-activated textiles, such as a polyester fibers coated withan epoxy adhesion enhancer, are typically used in combination with anRFL treatment to further improve the textile adhesion to rubbers.Although such pre-activated textiles perform well in many cases, thereremains a need for less expensive methods and compositions for adhesionpromotion between rubber and textile layers in order ultimately toproduce a reinforced, long-lasting, and durable rubber product.

[0005] Also worth mentioning are U.S. Pat. No. 5,064,876, to Hamada etal., and U.S. Pat. No. 5,082,738, to Swofford, both of which teach aprimer composition for promoting adhesion for polymer films. Suchdisclosed compositions comprise aminofunctional silanes. However,neither of these references teach the application of textiles to rubberformulations for reinforcement purposes nor do they teach or fairlysuggest the necessary combination of an amine functional group andanother organo-functional group, in particular a reactive group havingan affinity for rubber, as is now required within the inventivecomposition and method.

DESCRIPTION OF THE INVENTION

[0006] It is thus an object of the invention to provide improvedadhesion for a long-lasting and durable textile-reinforced rubberproduct. A further object of the invention is to provide a relativelyinexpensive method of achieved such improved adhesion. Another object ofthe invention is to provide an adhesion promoter which ultimatelyprovides a textile-reinforced rubber product which does not exhibitadhesive failure. Yet another object of this invention is to provide astable aqueous primer composition that, when applied before an RFLtreatment, activates the textile substrate in order to provide greatlyimproved adhesion to various rubber compounds.

[0007] Accordingly, this invention concerns a composition for promotingthe adhesion between a rubber composition layer and a textilereinforcing layer comprising

[0008] a mixture of at least two different silane compounds, at leastone compound selected from (I) and at least one compound selected from(II); wherein (I) and (II) include the following:

[0009] (I) aminosilanes selected from the group consisting of

[0010] wherein R is C₁-C₆ alkyl, R₁ is an amine functional group, and R′is an alkyl- or aromatic-acyl group;

[0011] (II) organo-functional silanes selected from the group consistingof

[0012] wherein R₂ is a group containing a radical selected from thegroup consisting of a mercapto moiety, a sulfide moiety, an isocyanatemoiety, an epoxy moiety, a pyridine moiety, a hydrophobic saturatedalkyl moiety, and a moiety having at least one unsaturated carbon-carbonbond, and R and R′ are defined as for (I) above. Nowhere within theprior art has such a specific adhesion promotor composition beendisclosed or practiced, particularly for activating textile substratesin order to improve adhesion to rubbers. Furthermore, nor has such aspecific composition or method of utilizing such a composition beentaught or fairly suggested. Such compositions and methods providesignificant advantages over the standard adhesion compositions andmethods of the state of the art.

[0013] Also, it has been discovered that a stable aqueous dispersion ofthe composition (a) above can be obtained without the use of anydispersing agents or surfactants. Component (II) of the inventivecomposition is not water soluble (some of the covered compounds can evenreact with water and thus are not stable in aqueous solution). Althougha water dispersion of the component (II) can be produced utilizingsurfactants, such dispersions have very limited shelf life. Besides, thesurfactants necessary to make such dispersions tend to affect adhesionadversely since surfactants are known to migrate to the interfaces andinterfere with the microscopic intimate contact between two unitingmaterials. However, by mixing components (I) and (II) together, thenslowly adding water to the mixture, a stable aqueous dispersion/solutioncan be obtained without utilizing any potentially deleterioussurfactants or dispersing agents.

[0014] The relative cost of the inventive compositions is very low atthe preferred level of usage, particularly when compared with thepre-activated textiles mentioned above. All of these characteristics andimprovements with the inventive compositions and methods thus translateinto lower costs for the user. Additionally, the inventive compositionsand methods can be utilized with any rubber compositions and with anytype of smooth filament textile normally utilized as a rubberreinforcement material. Examples of rubber compositions include, and arenot limited to, natural rubber, polyurethane rubber, styrene-butadienerubber (SBR), acrylonitrile-butadiene rubber (NBR), butyl rubbers,fluorinated rubbers, and ethylene-propylene-diene rubber (EPDM).Modified rubbers which are potentially useful, though more expensive,include hydrogenated SBR, hydrogenated NBR, and carboxylated NBR.Suitable textiles include, and are not limited to, those comprisingpolyester, polyester/cotton blends, polyamides, such as nylon-6 or -6,6,polyaramids (such as Kevlar®, available from DuPont), polypropylene,boron derivatives, glass fibers, and carbon fibers. The textilecomponent may be dyed or colored various shades and hues in order tofacilitate categorizing the different widths, lengths, etc., of productssuch as, without limitation, timing belts, and the like, forautomobiles. Finally, the inventive compositions and methods, whenutilized and/or practiced as intended, result in a textile-reinforcedrubber product which does not exhibit textile/rubber adhesive failure.

[0015] Preferably, the inventive composition comprises (I) anamine-functional silane component and (II) an organo-functional silanecomponent, which includes an unsaturated carbon-carbon bond. As notedabove, other reactive groups may be employed on the organo-functionalsilane component, such as, isocyanates, mercaptos, and epoxies, only asexamples. Being alkoxysilanes, also, both components (I) and (II)hydrolyze in the presence of water, then couple with either each otherand each with itself to form oligomers. It is therefore expected thatpre-hydrolyzed silane products can be utilized as substitutes forcomponents (I) and (II). Obviously some of the organic functional groupin component (II) will react with the amine group in component (I) uponmixing. However, it is the mixture of these two components thatgenerates the unexpected synergistic adhesion improvement which cannotbe achieved practically with either component alone.

[0016] Preferably, the inventive composition comprises a mixture of twoseparate compounds, an amine-functional silane (I) having the followingstructure:

R₁—Si(OR)₃  (I)

[0017] wherein R is C₁-C₆ alkyl and R₁ is an amine-functional grouphaving the molecular structure of

(NH₂R)(NHR)_(y)—Si(OR)₃

[0018] wherein R is defined for (I) as in Claim 1 and y is 0-4, and

[0019] an organo-functional silane (II) having the following structure:

R₂—Si(OR)₃  (II)

[0020] wherein R is C₁-C₆ alkyl and R₂ is a group having an unsaturatedcarbon-carbon bond. Of particular preference are (I)aminoethylaminopropyltrimethoxysilane, available from Dow Corning,Midland, Mich., and (II) 3-methacryloxypropyltrimethoxysilane, alsoavailable from Dow Corning. These particular compounds provide the bestadhesion promotion between textile substrates and rubber compositionsfor the lowest cost. Also, the amount of (I) and (II) is measured inweight ratios, with the preferred range being from about 1:1 [(I) to(II)] to about 100:1. Most preferred is a weight ratio of from about 2:1to about 10:1. The inventive composition may be present in a dispersion,either aqueous or non-aqueous, or in a neat solution diluted with anorganic solvent. An aqueous dispersion without any surfactants added ispreferred, as noted previously. The preferred concentration of silanesis from about 0.1 to about 5% on the weight of the fabric (owf) with apreferred range being from about 0.5 to about 2% owf. Furthermore, it ispreferred that, after the application of the inventive composition, aRFL treatment be used to increase the adhesive qualities of the entireproduct.

[0021] Any standard rubber additives, including ultraviolet absorbers,antioxidants, dyes, colorants, curing agents, perfumes, antistaticagents, fillers (such as carbon black), and the like may be added to therubber. To the textile substrate may be added any other standard textileadditives, such as dyes, colorants, pigments, ultra violet absorbers,antioxidants, and wetting agents. To the inventive composition and RFLused in combination with the inventive composition may be added wettingagents, antioxidants, filler dispersion (such as carbon black, silicaand ZnO dispersions).

[0022] The preferred inventive method of producing a textile-reinforcedrubber composite comprises the sequential steps of

[0023] (a) providing a textile substrate;

[0024] (b) contacting the textile substrate with a compositioncomprising either

[0025] (i) a mixture of at least two different silane compounds, onecompound selected from (I) and the other selected from (II); wherein (I)and (II) include the following:

[0026] (I) amine-functional silanes selected from the group consistingessentially of

R₁—Si(OR)₃

[0027]  or

[0028] wherein R is C₁-C₆ alkyl, R₁ is an amine-containing functionalgroup, and R′ is an alkyl- or aromatic-acyl group;

[0029] (II) organo-functional silanes selected from the group consistingessentially of

R₂—Si(OR)₃

[0030]  or

[0031] wherein R is C₁-C₆ alkyl, R₂ is a group containing a radicalselected from the group consisting essentially of a mercapto moiety, asulfide moiety, an isocyanate moiety, an epoxy moiety, a pyridinemoiety, a hydrophobic saturated alkyl moiety, and a moiety having atleast one unsaturated carbon-carbon bond, and R′ is the same as definedfor (I) above; or

[0032] (ii) at least one functional silane containing both anamine-functional group and a moiety having an affinity for rubber (suchas an unsaturated carbon-carbon bond);

[0033] (c) heating the textile substrate at a temperature of from about120 to about 250° C. for from about 15 seconds to about 5 minutes,preferably about 3 minutes;

[0034] (d) optionally coating or impregnating the textile substrate withan RFL composition;

[0035] (e) combining at least a portion of the resulting treated textilesubstrate with a rubber formulation to from a textile-reinforced rubbercomposite; and

[0036] (f) curing the textile-reinforced rubber composite.

[0037] In this process, contacting step (b) may be performed by anystandard, well known method, including dipping, padding, spraying,coating, impregnating, and the like. This silane pre-treatment of thetextile in essence “activates” the fibrous surface by effectivelycoating the textile with the adhesion promoter having reactive groupsand groups having affinity for the rubber layer oriented in a positionto facilitate the subsequent contact and adhesion of the rubber layerwith the textile layer. One of ordinary skill in the art wouldunderstand and be familiar with the addition and contacting of thesubject textile and rubber formulation with the potentially preferredRFL latex component as well as the rubber formulation contacting step(e), above. Furthermore, curing step (f) is performed in anyconventional manner, such as through heat-activated vulcanization in thepresence of a curing agent (such as organic peroxide). Again, such astep should be well within the purview of the ordinarily skilled artisanin this field.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0038] The Examples below are indicative of the particularly preferredembodiment within the scope of the present invention:

EXAMPLE 1

[0039] 7 parts of aminoethylaminopropyltrimethoxy silane and 3 parts of3-methacryloxypropyltrimethoxysilane were admixed in a beaker. To thismixture was slowly added a total amount of 1000 parts water in order toobtain a stable dispersion of silanes. Subsequently, the resultantdispersion was then transferred to a receptacle suitable for dippingfabric substrates. A 100% polyester sample of smooth filament fabric,cut into a few swatches of 2 inches by 12 inches and each swatch wasthen consecutively dipped into the dispersion, run through twocompressing rolls to squeeze out excess liquid, and then dried at 177°C. for 3 minutes in an oven. The fabric was then impregnated with aregular resorcinol formaldehyde vinylpyridine latex (formula provided bya technical bulletin released by Indspec of Pittsburgh, Pa., October,1991). A formulated and uncured SBR rubber was then sandwiched betweenthe two treated textile layers. The whole structure was then pressed atfour tons/m² pressure at 150° C. for 30 minutes. The resultant productobtained a cohesive peel strength of 36 lbs/inch. The peeling is termedcohesive because the resultant tearing occurred within the rubber itselfand did not result in an adhesive separation between the rubber and thetextile substrate.

EXAMPLE 2

[0040] The same procedure was followed as in EXAMPLE 1 except that themixture of amine-functional silane and methacrylic silane was replacedby 2-(vinylbenzylamino)-ethyl-3-aminopropyltrimethoxysilane. A peelstrength of 30 lbs/inch was obtained.

EXAMPLE 3

[0041] (Comparative)

[0042] The same basic procedure followed as in EXAMPLE 1 except that theRFL latex treatment was not utilized. A peel strength of 5 lbs/inch wasobtained.

EXAMPLE 4

[0043] (Comparative)

[0044] The same procedure was followed as in EXAMPLE 1 except that themixture of amine-functional silane and methacrylic silane was replacedby the aminoethylamino-propyltrimethoxysilane alone. A peel strength of24 lbs/inch was obtained.

EXAMPLE 5

[0045] (Comparative)

[0046] The same procedure was followed as in EXAMPLE 2 except that themixture of amine-functional silane and methacrylic silane was replacedby the methacryloxy-propyltrimethoxysilane alone. A peel strength of 15lbs/inch was obtained.

EXAMPLE 6

[0047] (Comparative)

[0048] The same procedure was followed as in EXAMPLE 1 except that theinventive mixture of silanes was not utilized and the RFL was the soleadhesive compound. The resulting peel strength obtained was 6 lbs/inch.

[0049] There are, of course, many alternative embodiments andmodifications of the present invention which are intended to be includedwithin the spirit and scope of the following claims.

What we claim is:
 1. A rubber/textile composite comprising a rubberadhered to a textile, said composite further comprising an adhesiveformulation located between said rubber layer and said textile layer,wherein said adhesive formulation comprises at least two differentsilane constituents and at least one RFL.
 2. The rubber/textilecomposite of claim 1 wherein at least one organo-functional silane ispresent and at least one amine silane is present.
 3. The rubber/textilecomposite of claim 1 wherein said composite exhibits a peel strengthupon curing of at least 30 pounds/inch.
 4. The rubber/textile compositeof claim 2 wherein said composite exhibits a peel strength upon curingof at least 30 pounds/inch.